Deoxygenation process for azomonoazine nu-oxide dyes



United States Patent Filed Apr. 12,1961, Ser. No. 162,372 5 Claims. c1. 26tl2t55) This invention relates to a new process for the deoxygenation of azomonoazine N-oxides.

More especially this invention relates to a process for deoxygenating arylazopyridine and quinoline N-oxides in a liquid halogenated hydrocarbon using a sulfur monohalide to yield the corresponding arylazomonazine.

Recently, arylazomonazines, especially amino-arylazomonazines have assumed great importance as intermediates for the preparation of cationic dyes for acrylic fibers. Consequently, various methods have been proposed for the preparation of these intermeditates. Probably the most favorable from the standpoint of liability of starting materials and potential over-all e ficiency involves the treatment of the corresponding N-oxides with an 1 -deoxygenation reagent to remove the oxide radical and yield the corresponding arylazomonazine. These N-oaddes are disclosed in commonly assigned, copending application Serial No. 765,326, filed October 6, 1958, now United States Patent No. 3,051,697.

For this purpose, a variety of procedures have been proposed. One such method heretofore employed for deoxygenating the N-oxide was to treat the N-oxide with iron powder in a polar solvent. While this method resulted in the desired arylazomonazine it has several disadvantages. It could not be employed where the l\- oxide starting material contained a free amino group since deoxygenation does not take place and the oxide is retained. Moreover, the use of the polar solvent is not desirable from a commercial standpoint, where the final objective is to otain a quaternized arylazomonoazine dyestuif for polyacrylonitrile.

Another method heretofore proposed was to treat the N-oxidc at low te eratures with phosphorus trichloride in a chlorobe zene. From a commercial standpoint, t-. process also has several drawbacks. Phosphorus trichloride is a d cult reagent to handle on a cornrnercial scale because it is a liquid having corrosive fumes. Moreover it is hazardous to use being highly toxic. In addition, this process results in poor yields.

Only about 65% of the final product is obtained whereas only 5% of the starting N-oxide material is recovered.

In attempting to arrive at a more commercially feasible process, some other generally applicable N-deoxygenetion processes also were assayed. One such process, known to be applicable to simple N-oxides such as Errol-oxide, employs as the deoxygenation reagent at least two moles of sulfur monocliloride per mole of the N-oxide, chloroform being used as the reaction medium. While yields from this process have been reported of the der of 80% of theoretical for some purposes, in practice it was found generally to result in yields of a much lower order. Application of this procedure to arylazomonazine N-oxides, such as are treated herein, afforded only a dark, unidentifiable mass having 206% of the expected weight. No arylazornona- Zine could be isolated therefrom.

There remains, then, a demand for a process whereby N-oxides of arylazomonazines can be deoxygenated in high yields without the disadvantages which are attendant upon the prior art processes. It is a principal ob- Billllh Patented .lan. '3 1964 ject of this invention to fill this demand. Further oboxides are deoxygenated by a process which comprises contacting the N-oxide in a liquid halogenated benzene medium with a sulfur monohalide. While tne invention may be thus simply stated, there are a number of factors which must be controlled each within its own limits for successful operation. These include the choice and amount of solvent; the reactant proportions; temperature of reaction and the like.

It is a feature of this invention that a wide variety of arylazomonazine-N-oxides can be successfully treated in the process thereof. To illustrate the starting materials without limiting the scope of the present invention, the following arylazomonazine N-oxide starting materials may be named:

2- (p-aminophenylazo -pyridinel-oxide,

2- (p-dimethylaminophenylazo) -pyridine-1-oxide, Z-(p-acetaminophenylazo) -pyridine-1-oxide,

2- (4-arninol-naphlhyl azo) pyridine- 1 -0Xide,

3- (p-diethylarninophenylazo -pyridine-1-oxide, 4-(parninophenylazo) picoline-l-oxide,

2- (p-dipropylamino-o-tolyazo) quinolinel-oxixde, 2-(o--acetaminop-aminophenylazo -pyridine-1-oxide.

Some of these N-oxides are relatively new in the art, forming part of the subiect matter of the commonly assigned, copending application Serial No. 765,326, filed Qctober 6, 1958, for the production of azonionazine N- oxides. As shown therein, they may be prepared by diazotizing a 2-aminomonazine-N-oxide and coupling it to any desired aryl coupling component, especially one having an electron-releasing group in the position ortho or para to the position coupled.

Suitable halogenated benzenes for the purpose of the present invention are chlorinated benzenes such as monochlorobenzene, o-dichlorobenzene, rn-dichlorobe nzone and 0-, rnor p-tolyl chloride; brominated benzenes such as monobromobcnzene, o-dibromobenzene, m-dibromobenzene and 0- or m-tolyl bromide; and monoiodo benzene, o-diiodobenzene, and 0- or m-tolyl iodide. Other halogenated benzenes may be used.

Any available sulfur monohalide may be used for the deoxygenation of the cl-oxide; sulfur monochloride is preferred to other halides in View of its availability.

From about 0.25 to about 1.5 moles of sulfur monohalide are used for each mole of N-oxide which is treated. It is preferred that between about 0.5 and about 1.1 moles of sulfur monohalide be employed since in this range, somewhat higher quality products are obtained. Thus, when the products are used directly as dye intermediates dyes of somewhat cleaner shades result.

The temperatures at which the reaction occurs successfully, vary over a wide range, depending on the par.- ticular N-oxide which is treated and on the solvent which is employed. Generally, the reaction can be conducted at temperatures as low as about -35 and as high as about C. For convenience the temperature is nor-1 mally kept below the reflux temperature of the solvent and usually in the range of about 20 to about 50 C,

The process is preferably conducted by dissolving the arylazornonazine N-oxide in the halogenated benzene solvent, using sufficient solvent and some heat if necessary to insure complete solution. Normally about 10 to about parts or more by volume of solvent per part of N-oxide are used depending upon the solubility of the N-oxide. The sulfur monohalide (e.g., the chloride) is added to the solution and the mixture then allowed to stand, with or without stirring, as desired, until the reaction has proceeded to substantial completion. Reaction times will vary, but the reaction will generally be completed between one-half and two hours. The product can be isolated from the reaction mixture by alkalinization and filtration of the resultant water-insoluble base. Further purification can be practiced as desired.

The new improved sulfur monohalide process of this invention gives a high quality product in much higher, almost quantitative, yields.

The deoxygenated product obtained in accordance with the present invention can be converted to useful dyes for polyacrylonitriles by treatment with an alkylat ing agent as disclosed in commonly assigned copending application Serial No. 764,239, filed September 30, 1958.

Thus an alkylating agent such as dimethyl sulfate in equimolecular amount is added to the monohalogenated benzene filtrate containing the deoxygenated product.

The solution may then be warmed to complete the quaternization. Temperatures of about 5660 C. may be used or possibly higher, depending on the al kylating agent. On cooling, the quaternized azo dye product precipitates and is isolated by filtration and washed with monochlorobenzene.

An example of deoxygenation followed by quaternization is as follows:

The quaternized products (i.e.; cationic dyes for polyacrylonitriles) obtainable in this way are of very high quality. Yields both for deoxygenation and quaternization are nearly theoretical. The quaternized product shown above, dyes fibers of polyacrylonitrile a bright reddish violet shade.

The following examples illustrate this invention. Parts are by weight unless otherwise noted.

Example 1 To 200 parts of chlorobenzene is added 5.93 parts of 2-(4-dirnethylaminophenylazo)-pyridine-l-oxide and the mixture is heated at 50 C. until solution is obtained. The solution is cooled to 30 C. and 6.7 parts of sulfur monochloride (S Cl added at once. The mixture is heated to 50 C. and held at this temperature until deoxygenation is complete (30 to 50 min). It is cooled to 25 C. and a solution, prepared by mixing 16 parts of 50% sodium hydroxide solution with 100 parts of water, is added. The resultant mixture is stirred for a short time; 2 parts of a filter aid are added and after further stirring the whole is clarified. The sludge is washed with 50 parts of monochlorobenzene and this Wash is combined with the filtrate. The monochlorobenzene layer, containing the desired product is washed with water until the washings are neutral to Brilliant '4 Yellow indicator paper. A sample of the chlorobenzene layer analyzed by a visual spectrophotometric method shows 98% deoxygenation to 2-(4-dirnethylaminophenylaZo)-pyridir1e.

The product is isolated in the form of a quaternary salt in the following way: The chlorobenzene solution is dehydrated by azeotropic distillation in vacuo at 60 C. An equimolecular amount of dimethyl sulfate, 1.85 parts by volume is added to the chlorobenzene solution containing the product at 30 C. The mixture is heated to 65 C. and held at this temperature until quaternization is complete. It is then cooled to 25 C. and the product, 2-(4-dimethyiaminophenylazo)-1methyl pyridinium methosulfate isolated by filtration, washed with chlorobenzene and dried at The product dyes polyacrylonitrile a reddish violet.

Example 2 To 400 parts by volume of chlorobenzene is added 12 parts of 2-(4-dimethylaminophenylazo)-pyridine-loxide and the mixture stirred at 50 C. until solution is obtained. The solution is cooled to 25 C. and main tained at this temperature while 6.64 parts of sulfur monochloride are added. The whole is stirred at 25- 30 C. until deoxygenation is complete (2 hrs). A solution of 32 parts of 50% sodium hydroxide solution and 100 parts of water is added. After stirring a short time, 6 parts of a filter aid are added and after further stirring, the whole is filtered. The chlorobenzene layer containing the deoxygenated product, 2-(4-dimethylaminophenylazo)-pyridine, is separated and washed with 5% sodium bicarbonate solution and then with water until the pH of the washings is 7. It is then separated and dehydrated in vacuo using the method of Example 1. An equimolecular amount of dimethyl sulfate, 4.45 parts by volume, is added and the mixture stirred at 65 C. until quaternization is complete. It is cooled to 25 C. and the quaternized product isolated by filtration, washed with chlorobenzene and dried. An overall quantitative yield is obtained. The product dyes acrylonitrile bright violet shades.

If in the above example, 664 parts of sulfur monochloride is replaced by 11.5 parts of sulfur monobromide, the same product is obtained.

Example 3 To 400 parts of chlorobenzene is added 12 parts of the starting material of Example 1. After dissolving at 50 C. the solution is cooled to 2025 C. and 6.64 parts of sulfur monochloride is added. The whole is stirred for one hour at 25-3G C. and then for two hours at 60 C. It is then cooled to 25 C. 200 parts by volume of 10% sulfuric acid are added and the mixture stirred for two hours. The acidic layer is separated, clarified and made alkaline with 50% sodium hydroxide solution. The product which separates, is filtered, washed with Water and dried to yield 2-(4-dimethylaminophenylazo -pyridine.

Example 4 If, in Example 2, 400 parts by volume of monochlorobenzene is replaced by 250 parts by volume of ortho diodo benzene, and the deoxygenation run at about 15 C. the deoxygenated product 2-(4-dimethylaminophenylazo)-1-methyl-pyridinium sulfate, dyeing polyacrylonitrile a red violet, is obtained.

Example 5 If in Example 2, the 400 parts by volume of monochlorobenzene is replaced by 500 parts by volume of monobromobenzene and the deoxygenation run at about 15 C. the same deoxygenated product as mentioned in Example 4, is obtained.

Example 6 If in Example 1 the sulfur monochloride is replaced with an equivalent amount of sulfur monoiodide the same product of high purity in about the same yields is obtained.

I claim:

1. A process of deoxygenating an azomonazine N- oXide selected from the group consisting of aminophenylazopyridine N-oxides, aminonaphthylazopyridine N-oX- ides, aminophenylazoquinoline N-oxides and aminonaphthylazoquinoline N-oxides wherein the amino moiety is selected from the group consisting of primary amino, lower alkylamino and acetamide which comprises treating the N-oxide at a temperature in the range of 35 C. to 75 C. in a liquid halogenated benzene solvent wherein the halogen atoms are selected from the group consisting of chlorine, bromine and iodine, with 0.5 to 1.5 moles of sulfur monohalide per mole of said N-oxide, said sulfur monohalide being selected from the group consisting of sulfur monochloride, sulfur monoiodide and sulfur monobromide.

2. A process of deoxygenating a Z-(p-dimethylaminophenylazo)-pyridine-1-oxide which comprises treating said N-oxide in chlorobenzene at a temperature range of 35 C. to 75 C. with 0.5 to 1.1 moles of sulfur monochloride per mole of said N-oxide 3. A process of deoxygenating a Z-(p-acetamidophenylazo)-pyridine-1-oxide which comprises treating said N- oxide in chlorobenzene at a temperature range of 35 C. to 75 C. with 0.5 to 1.1 moles of sulfur monochloride per mole of said N-oxide.

4. A process of deoxygenating a 2-(o-acetamido-paminophenylazo)-pyridine-1-oxide which comprises treating said N-oxide in chlorobenzene at a temperature range of 35 to 75 C. with 0.5 to 1.1 moles of sulfur monochloride per mole of said N-oxide.

5. A process of deoxygenating a Z-(p-dipropylamino- I o-tolylazo)-quinoline-1-0Xide which comprises treating said N-oxide in chlorobenzene at a temperature range of 35 C. to 75 C. with 0.5 to 1.1 moles of sulfur monochloride per mole of said N-oxide.

References Cited in the file of this patent Furukawa, Chem Abs 50 8639a (1956). 

1. A PROCESS OF DEOXYGENATING AN AZOMONAZINE NOXIDE SELECTED FROM THE GROUP CONSISTING OF AMINOPHENYLAZOPYRIDINE N-OXIDES, AMINONAPHTHYLAZOPYRIDINE N-OXIDES, AMINOPHENYLAZOQUINOLINE N-OXIDES AND AMINONAPHTHYLAZOQUINOLINE N-OXIDES WHEREIN THE AMINO MOIETY IS SELECTED FROM THE GROUP CONSISTING OF PRIMARY AMINO, LOWER ALKYLAMINO AND ACETAMIDE WHICH COMPRISES TREATING THE N-OXIDE AT A TEMPERATURE IN THE RANGE OF -35* C. TO 75*C. IN A LIQUID HALOGENATED BENZENE SOLVENT WHEREIN THE HALOGEN ATOMS ARE SELECTED FROM THE GROUP CONSISTING OF CHLORINE, BROMINE AND IODINE, WITH 0.5 TO 1.5 MOLES OF SULFUR MONOHALIDE BEING SELECTED FROM THE GROUP CONSISTING OF SULFUR MONOCHLORIDE, SULFUR MONOIODIDE AND SULFUR MONOBROMIDE. 